The invention relates to a method for securing a machine tool comprising a first tool part that carries out work movements in the direction of a second tool part in order thereby to carry out a machining process on a workpiece, wherein an optoelectronic sensor monitors a three-dimensional protected field between the tool parts in that light is transmitted along an open gap formed between the tool parts by means of a transmitter device and is detected by means of a receiver device which includes a matrix of light-sensitive elements, wherein the first tool part is stopped if individual light-sensitive elements or specific groups of the light-sensitive elements do not receive any light. The invention furthermore relates to an optoelectronic sensor for carrying out such a method.
The named machine tool is typically a stamping press for the bending, folding, cutting or stamping of workpieces such as sheet metal parts. The named first tool part is formed in this case by a top tool which has a longitudinal bending line or cutting edge. This top tool is moved, during its working movement, vertically downwardly toward a bottom tool which serves as a second tool part and which the workpiece contacts or lies on.
For each machining process, the previously machined workpiece must first be removed and the new workpiece to be machined must be introduced into the open gap between the tool parts. This is done manually by an operator as a rule. To avoid an injury to the operator, in particular to his hands, by a dangerous movement of a part of the machine tool during the closing of the open gap, the optoelectronic sensor monitors a protected field which typically extends beneath the moved top tool. This protected field is three-dimensional, i.e. at least its outline extends along a two-dimensional cross-section such that the sensor can react fast and reliably to dangerous intrusions from different directions and can trigger a stopping of the dangerous movement.
In addition to the named optoelectronic sensor, separate measuring devices are frequently provided in machine tools known from the prior art which are suitable for a measurement of the machined workpiece. It can, for example, be determined by means of such measuring devices whether a machining process was carried out correctly and without error on a workpiece.